This research investigated the effect of aspect ratios (evaporator length to inner diameter of capillary tube), inclination angles, and concentrations of silver nanofluid on the heat transfer rate of a closed-loop oscillating heat pipe with check valves (CLOHP/CV). The CLOHP/CV was made from copper tubing with an internal diameter of 2 mm. Two check valves were inserted into the tube. The tube had 40 meandering turns. The length of the evaporator was 50, 100, and 150 mm. The lengths of the evaporator, adiabatic, and condenser section were equal. The concentration of silver nanofluid was 0.25, 0.5, 0.75, and 1 %w/v, and the operating temperature was 40, 50, and, $60^{circ}C$. It was found that the heat transfer rate of the CLOHP/CV using silver nanofluid as a working fluid was better than that the heat transfer rate when pure water is used because the silver nanofluid increases the heat flux by more than 10%.